A-LEVEL
BIOLOGY
BIOL2 – The variety of living organisms
Report on the Examination
2410
June 2016
Version: 0.1
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REPORT ON THE EXAMINATION – A-LEVEL BIOLOGY – BIOL2 – June 2016
General comments
Generally speaking, student achievement on this Unit was in line with previous years, with a
slightly lower mean mark but similar spread.
Students’ knowledge of some definitions was surprisingly patchy and many answers lacked
precision in the use of technical terms. The question testing knowledge and understanding of a
practical skill suggested many students had not carried out this kind of work and surprisingly few
students demonstrated that they had a sound knowledge about the pattern of blood circulation in
mammals, which may be regarded as being a basic concept.
Answers demonstrated that students’ understanding is secure about natural selection and the
requirements of cellular respiration. Students showed skill in translating information from tabulated
or chart form into continuous prose, and they showed some awareness of how science has
affected attitudes in our society.
Question 1
(a)(i)
Only about two thirds of students were able to define successfully the term ‘phylogenetic
group’. Many explained why organisms are placed into an individual group without
defining the term.
(a)(ii)
A majority of students achieved both marks for the definition of ‘species’. That members
of the same species produce fertile offspring is well understood, although some students
regarded ‘mating’ as equivalent to ‘reproduction’, which cost them a mark.
(b)
Ordering of the phylogenetic groups is very well understood, with very few failing to
achieve a mark. Phonetic spellings of these common biological terms was frequent.
(c)
Students demonstrated a good understanding of the non-overlapping nature of genus
and species groupings by drawing concentric circles with no intersect. Many failed to
draw a separate circle for each genus so achieved only a single mark because they had
not made full use of all the information given in the table.
(d)
Most students used the information on base sequences correctly to identify the closer
phylogenetic relationship between Sumatran and South China tigers without always
stating clearly that their common ancestor was more recent or the tigers are more
closely related. Some gained no mark by making a comparison in which they said the
nucleotide sequences were ‘similar’ rather than ‘identical’.
Question 2
(a)
Most correctly identified ‘quaternary’ as the appropriate term to describe the protein’s
structure with ‘tertiary’ being a common misconception.
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(b)
The triplet nature of the DNA nucleotide code for amino acids is well understood. Very
few failed to achieve the mark, although some students divided by three instead of
multiplying by three.
(c)
Detailed accounts of haemoglobin’s allosteric properties, its structure, the Bohr shift or
the number of oxygen molecules loaded per molecule were common, demonstrating
where students had not read carefully enough the detail required in this question. Where
students achieved only a single mark, they had usually not referred precisely to the
location where haemoglobin associates with oxygen.
(d)(i)
A vast majority of students successfully used the graph to find the correct difference in
percentage saturation of haemoglobin with oxygen. A few failed to gain the mark despite
having identified the correct values on the graph because they calculated a percentage
change, rather than the difference.
(d)(ii)
This question discriminated well. Students who understand the transport of oxygen topic
gave good responses that made clear a link to the context of anaemia with a sense that
the shortage of haemoglobin molecules would, to some extent, be compensated for by
the reduced oxygen affinity. Some did not make a direct reference to ‘reduced affinity’
although they demonstrated a good understanding of the principle. Occasionally
students went off at a tangent by referring to the effects of altitude differences and some
erroneously described the curve’s shift to the right as representing an ‘increase’ in
affinity.
Question 3
(a)
Almost as many achieved this mark as did not, so the definition of species diversity is
not well known. Some confusion exists between species diversity and genetic diversity.
Many students referred incorrectly to diversity within a ‘population’ so missed completely
the point that the definition focussed on a collection of species. Instead of using ‘number’
in their definition, some students mentioned ‘range’ to suggest that they regarded
diversity as a measure between two extremes.
(b)
Most students achieved a mark for demonstrating they knew that the number of each
species is relevant in the calculation, but, for many, their poor quality of written
communication prevented the award of a second mark. For example, a common error
was to refer to ‘number of species’ rather than make clear the importance of a ‘grand
total of organisms’.
(c)
Many students showed a good appreciation of the principles of diversity and density and
achieved both marks. The imprecise use of terms prevented some from achieving any
marks, eg, ‘organism’ rather than ‘species’; ‘thrive’ rather than ‘reproduce’ and ‘hostile’
rather than a precisely described effect of sewage.
(d)(i)
The principle that repeatable results are a requirement in order to be able to draw
conclusions was well understood. Unfortunately, some students only offered a comment
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about the observed difference in results and did not go further to state that it prevented
the scientist from coming to a conclusion. Others gave an imprecise comment about the
scientist being less able to draw a conclusion or they gave reasons why the two
investigations might have produced differing results or they offered suggestions on how
to improve the quality of findings.
(d)(ii)
Very few students gained the mark here either because they referred only to making a
‘single repeat’, or they repeated the investigation by changing the independent variable,
and hardly any went further to confirm what the repeats would need to show before
conclusions could be made.
Question 4
(a)(i)
Approximately two thirds of students knew this term and could spell it correctly.
(a)(ii)
Many more students were successful in naming ‘tracheoles’ precisely than in naming
‘spiracles’ in 4(a)(i).
(b)
This question discriminated well. Often a lot of unnecessary detail was given about the
structure of the tracheal system. Relatively few students mentioned how cellular
respiration established the oxygen diffusion gradient and much time was wasted by
some in explaining the movement of carbon dioxide. Lungs are thought by more than a
minority of students to be insect structures.
(c)
Even the ablest of students sometimes gained just a single mark for identifying, and
often describing at length, that the chart showed a correlation existed between
abdominal pumping and carbon dioxide release. They did not go further to explain what
caused the correlation, namely that pressure increased when tubes are squeezed.
Having established that a gradient of pressure existed in the tubes, some able students
then, incorrectly, referred to diffusion being the mechanism of gas transport. As with
BIOL1, examiners suggested there is patchy understanding of differences between the
concepts of diffusion and mass flow. Many thought that pumping was a cause of
increased carbon dioxide concentration rather than being a response to it and a common
misconception was for carbon dioxide production to generate a diffusion gradient which
led to its release.
Question 5
(a)
Approximately half of all students achieved one mark on this question and about a fifth
achieved both. A lack of awareness of homologous chromosomes and their role in cell
division was a common feature throughout the different parts of question 5.
(b)
Some students gave a concise description for, and explanation of, the appearance of
chromosome K, although few made a reference to DNA replication for the presence of
two chromatids. Some students offered two points of description without giving an
explanation of either.
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(c)
The idea of ‘crossing over’ is well understood, although not what structures it occurs
between. Few stated that homologous chromosomes are involved (some referred
vaguely to maternal and paternal chromosomes), although occasionally references to
bivalent or non-sister chromatids demonstrated that there is an awareness of the
principle. Independent assortment and crossing over are biological processes which
some students confused.
(d)
Some sensible suggestions gained credit, like cell D is the product of division in cell B, or
cell D is the result of Meiosis I, but many answers included long and tortuous accounts
that confused fundamental differences between mitosis and meiosis. Structures were
inaccurately referred to as chromatids and the idea that a homologous chromosome ‘is
split’ is a fairly common misconception.
(e)
Just under half of all students achieved this mark to show that there is good awareness
about the position of DNA replication in students’ understanding of the cell cycle. Many,
however, said DNA levels per cell would change during the different stages of mitosis.
Question 6
(a)
Very few students had a good understanding of the term ‘temporary mount’, used in this
question, although it is a term stated on pages 18 and 20 of the specification. Some
students thought it is a structure inside a leaf. These answers suggest that this kind of
practical work is not a common activity. Often, vague references that enabled some to
accumulate marks were made to ‘rectangular glass pieces’ and ‘cover slides’, although
few included keeping the specimen moist or staining it before applying a coverslip.
(b)
Accurate measurements and appropriate calculations were performed by the vast
majority of students.
(c)
Surprisingly, only 5% of students achieved full marks on this question. Again, there was
confusion about the meaning of ‘temporary mount’ which some students regarded to be
a type of cell; they suggested counting chloroplasts in many temporary mounts. Many
misread the question and so estimated the total number of chloroplasts in a leaf rather
than estimate a mean number of chloroplasts in cells. Hardly any students demonstrated
an awareness of the need to select cells at random or choose a large number of cells to
use in their investigation. For many, the only mark achieved was for making a statement
about counting chloroplasts.
(d)
As many students answered this question correctly as got it wrong. This suggests there
is a lack of understanding about the concept of cell organisation which prevented many
from applying their understanding appropriately to the context given in this question.
Incorrect responses included organelle, tissue (frequently), totipotent, specialised and
organ system.
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REPORT ON THE EXAMINATION – A-LEVEL BIOLOGY – BIOL2 – June 2016
Question 7
(a)
Over three quarters of students correctly identified ‘locus’ as the position of a gene on a
chromosome with ‘allele’ and ‘exon’ given frequently as incorrect answers.
(b)
Most students correctly defined the term ‘genetic diversity’, usually by referring to the
number of different alleles. ‘Genes’ was used instead of ‘alleles’ by more than a few and
some tried to hedge their bets by quoting ‘genes/alleles’. Imprecise expressions like ‘the
range of alleles’, ‘variation of alleles’ or ‘number of alleles’ were not credited, but often
seen.
(c)
This question tested students’ ability to select and translate appropriate information from
tabulated form and it differentiated well. Most achieved two marks and many got all
three. Concise reference was often made to ‘overlapping standard deviations showing
no significant difference between mean values’ and demonstrated that there is sound
awareness of this principle. Nevertheless, some misread the table and quoted Airedale
as being the most diverse and others failed to make a comparison, but relied simply
upon using a list of numbers. Occasionally, students failed to identify the breed of dog in
the comparison they made, leaving the onus on the examiner to decipher what they
really meant. Some commented correctly on ‘low values of standard deviations showing
that there was high reliability’, but this did not answer the question. Misconceptions, such
as ‘high diversity shows more genes are involved’ and ‘overlapping standard deviations
show breeds are closely related’ were not uncommon.
(d)
This question proved beyond most students because they did not link the data to human
involvement in the selective breeding of domesticated animals. Many thought incorrectly
that frequent mutations caused the changes in genetic diversity, and many thought
speciation had occurred which involved isolating mechanisms such as island populations
or river barriers. Some put the changes down to environmental causes. Reproducing
Miniature terriers with other breeds was often correctly given to indicate that they were
more outbred, and ‘selection of specific traits in Bull terriers’ was accepted at the lowest
level for inbreeding. References to a gene pool or to changes in the number of different
alleles were rare. Some students referred to the terriers as different species, but then
bred them and their offspring successfully, which suggested there is a misconception
with the concept of species.
Question 8
(a)
In this question, students were required to look critically at the results of other scientists.
Unfortunately, many insisted on making comments about the maximum increase in
percentage blood flow despite being told not to do this. Most achieved one mark for
correctly identifying the kind of meal that caused the quickest or slowest changes in
blood flow, but very few looked at the data sufficiently closely to notice that there was
wide variation between the values.
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(b)
This question differentiated very well and many students demonstrated a secure
understanding about the principles of demand and supply in the context of cellular
respiration. Many answers were full and logically sequenced. A common misconception
was that respiration ‘stops’ in the gut if exercise occurs because blood is ‘not required’
there, or respiration ‘begins’ in muscles when they are involved in exercise. Sadly, once
again, some students referred to the production of energy rather than to its release.
(c)
Students achieved a good mix of all the marking points available for this question without
often combining them into a logical sequence. The best answers were seen when
students looked directly at the values given in both the table and also the figure and
made comparisons between them, but they rarely extended their answer further than
this. Many wrote at length using poorly punctuated long sentences, the meaning of
which examiners found challenging to decipher. Rather than focus on the information
given, many students discussed the design of the investigations, which was not
required. Unfortunately, good answers were commonly spoiled when students
suggested a reduced blood flow would affect digestion rather than restrict absorption.
Comments on the effect of a meal on the time taken to change blood flow tended not to
be linked with precision to the timings shown in Figure 7.
(d)
This question gave students an opportunity to sequence their knowledge on what was
intended to be a straightforward test of a basic concept. This assumed, of course, that
this knowledge is secure. Unfortunately, in many answers it was apparent that the
pattern of circulation is not well known. The relative position of arteries and veins was
incorrectly juxtaposed around organs, hepatic blood vessels were incorrectly linked to
the kidneys, and veins were said to deliver blood into ventricles rather than into the atria.
Hardly any students mentioned that capillaries in the lungs connected the arterial and
venous blood supply. Many did not indicate which side of the heart was involved in blood
movement. It was not uncommon for blood to be described flowing in a series
arrangement between the liver and the kidneys. Those students who achieved only one
mark usually did so because they knew the pulmonary artery took blood to the lungs; it
was by far the best known of all the marking points.
Question 9
(a)
Most students demonstrated a sound understanding of the principle that a hypothesis is
a statement that is tested by an investigation. Predictions were most often given and
many gave null hypotheses. Marks were missed when students failed to make any
reference to ‘resistance’ in the context of bacteria, and it was not uncommon for the
resistance to be linked to the animal or human rather than to Escherichia coli.
(b)(i)
Many students showed good skill and precision by selecting the right information from
Table 6 and made careful references to ‘percentages’ and ‘resistance’ to gain full marks.
(b)(ii)
The principle of natural selection is well understood, but often marks were missed
because of a misconception that antibiotics cause mutations. Imprecise expressions
were common, such as ‘bacteria thrive’ or they ‘grow’ rather than they ‘reproduce’.
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REPORT ON THE EXAMINATION – A-LEVEL BIOLOGY – BIOL2 – June 2016
Occasionally, students wrote that ‘resistant alleles survived’, with no role implied for the
bacteria that contained them.
(c)
Approximately a quarter of students achieved the mark on this question because they
made a clear link between human faeces and contaminating pathogens. Many
mentioned Escherichia coli, which the question explicitly told them not to do, and poor
written communication was evident in answers suggesting that what is spread is a
‘disease’ rather than an ‘agent of disease’.
(d)
The principle of measuring the reliability of the design of an investigation is very well
understood, with the majority of answers gaining two marks. Some students misread the
question because they suggested changes in the design to increase reliability, and
others did not notice ‘reliability’ was given in the question’s stem so it should not have
been included as an answer.
(e)
This question differentiated well. Students made appropriate suggestions using either
DNA hybridisation or nucleotide sequencing to address the context of this question;
some wrote at length about both of these techniques. A minority of responses discussed
using antibodies to compare the similarities, possibly they think DNA is a kind of protein.
(f)
Few students achieved more than three marks on this question because many tended to
dwell far too long on giving a full explanation of how natural selection increased cases of
resistance; they did not look to give broader reasons relating to society’s view.
Contamination of the human food chain, avoiding adverse side effects, the generation of
superbugs, and high costs were common answers, although students giving more than
any two of these was rare. Very few answers contained suggestions about changes in
legislation and, although prevention of the horizontal and vertical transmission of genes
conferring resistance was often cited, it was rare for students to make clear the principle
of avoiding transmission of resistance into other harmful bacteria, so this marking point
was not often awarded.
Mark Ranges and Award of Grades
Grade boundaries and cumulative percentage grades are available on the Results Statistics
page of the AQA website.
Converting Marks into UMS marks
Convert raw marks into Uniform Mark Scale (UMS) marks by using the link below.
UMS conversion calculator
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